This invention relates to trouble-detecting, trouble-judging and failsafe devices in a system for integrally controlling an automatic transmission and an engine.
Automatic transmissions comprising gear transmission mechanisms, a plurality of frictionally engaging devices, and hydraulic pressure control devices operated to selectively switch the engagements of the frictionally engaging devices, so that any one of a plurality of gear stages can be achieved in accordance with a preset shift map, are well known in the transmission art.
Furthermore, in an automatic transmission for a vehicle, of the type described, various systems are known for integrally controlling an automatic transmission and an engine, wherein, engine torque is changed during shifting to obtain satisfactory shift characteristics and durability of the frictionally engaging devices.
When the engine torque is changed during shifting, absorbed energy in members and in the frictionally engaging devices for braking these members in the automatic transmission can be controlled. As a result, the shifting can be completed with low shocks for a short period of time, so that a satisfactory shift feeling can be given to a driver and the durbility of the frictionally engaging devices can be improved.
Now, in constructing the above-described system, when means for controlling the engine, means for controlling the automatic transmission and further control means for changing the engine torque by a predetermined value as commensurate to the shifting of the automatic transmission are integrally provided, such problems are presented that increased capacity of a computer leads to increased cost and it is disadvantageous to mount the system on a vehicle which has a high limitation in storage space.
Furthermore, adoption of the integrally controlling system may be disadvantageous from the viewpoints of commonuse properties and general-purpose properties, because there are vehicles which require no engine change.
To obviate the above-described disadvantages, there is proposed a technique wherein the aforesaid control means are separately provided (for example, Japanese Patent Application No. 105543/1986: this is not of the prior art).
However, when the means for controlling the engine and the means for controlling the automatic transmission are formed separately of each other as described above, in order to change the engine torque during shifting for example, it becomes necessary to provide communication lines which connect both control means to each other. The provision of these communication lines presents such a problem that these communication lines may be disconnected or short-circuited. As a result, an engine torque change control cannot be adequately carried out in a case where the engine torque change control should be performed. If the aforesaid situation occurs, then an amount of absorbed energy in the frictionally engaging devices on the automatic transmission side increases, whereby the durability of these frictionally engaging devices is deteriorated. Furthermore, the shift duration is prolonged, whereby the shifting is not completed within a shockless region of an accumulator, so that shift shocks become high. This is because, on the automatic transmission side, shift turning data such as oil pressure are preset in expectation of decrease in the engine torque by a predetermined value during the shifting.
As a consequence, it is necessary to detect troubles in these communication lines as soon as possible and accurately. Further, the detected troubles should be appropriately coped with.